In public facilities or large private facilities, there are several different types of metering faucets in use today. Many are manually activated to turn on the water by pressing the faucet head and are hydraulically timed so that the water remains on for a set period of time after depression of the head. Some of these faucets have separate head allowing separate control over the hot and cold water. Other metering faucets mix the incoming hot and cold water streams and, when actuated, deliver a tempered output stream.
Also known is a manually activated metering faucet whose on-time is controlled electronically. Still other known faucets are activated electronically when the user positions a hand under the faucet. Automatic water dispensing systems have provided numerous advantages including improved sanitation, water conservation, and reduced maintenance cost. Since numerous infectious diseases are transmitted by contact, public-health authorities have encouraged the public and mandated to food workers the exercise of proper hygiene including washing hands effectively. Effective hand washing has been made easier by automatic faucets. Automatic faucets typically include an object sensor that detects presence of an object, and an automatic valve that turns water on and off based on a signal from the sensor. If the water temperature in an automatic faucet is not in an optimal range, individuals tend to shorten their hand washing time. To obtain an optimal water temperature, a proper mixing ratio of hot and cold water and proper water actuation has to be achieved. Automatic faucets usually use a preset valve that controls water flow after mixing.
The hydraulically timed faucets are disadvantaged in that it is difficult to accurately control the on-time of the faucet over the long term because of mains pressure changes and foreign matter build up in the faucet which can adversely affect the hydraulic controls within the faucet. On the other hand, the known electronic faucets can not always discriminate between a user's hand and other substances and objects which may be brought into proximity to the faucet, e.g. a reflective object disposed opposite the faucet's infrared transceiver, soap build up on the faucet's proximity sensor, etc. Resultantly, those prior faucets may be turned on inadvertently and/or remain on for too long a time resulting in wastage of water.